1. Field of the Invention
The invention relates to a decoder in a communication system, and in particular to an add-compare-select (ACS) unit in a decoder and a method thereof.
2. Description of the Related Art
Convolutional encoding is typically utilized in digital communication systems to combat noise and interference during data transmission. Convolutional encoded data is recovered by a convolutional decoder in a receiver. A Viterbi decoder is a convolutional decoder used to achieve the maximum likelihood of decoding convolutional codes, by selecting a code sequence from a plurality of possible code sequences to decode the received data. An add-compare-select (ACS) unit is the key functional unit of a Viterbi decoder. The ACS unit compares the probability of all possible code sequences to decide a most likely sequence. The convolutional decoder may be implemented with pipelining, look-ahead, and parallelism techniques to enhance computation speed and circuit performance. These techniques, however, increase circuit complexity, circuit dimensions and manufacturing cost.
Thus an ACS unit and a method capable of minimizing circuit dimensions, without degrading circuit performance incurred by the use of pipelining, look-ahead, and parallelism techniques are desirable.